The Insidious Big Brother Database (BBDB) is a contact management utility for use with GNU Emacs and XEmacs. It can hook into Emacs-based mail- and news-readers and automatically collect information on messages therein.

CMUCL is a free, high performance implementation of the Common Lisp programming language which runs on most major Unix platforms. It mainly conforms to the ANSI Common Lisp standard. CMUCL provides a sophisticated native code compiler; a powerful foreign function interface; an implementation of CLOS; the Common Lisp Object System; which includes multimethods and a metaobject protocol; a source-level debugger and code profiler; and an Emacs-like editor implemented in Common Lisp. CMUCL is maintained by a team of volunteers collaborating over the Internet, and is mostly in the public domain.

crypt++.el is a package of Lisp functions that
recognize automatically encrypted and encoded
(i.e., compressed) files when they are first
visited or written. The BUFFER corresponding to
the file is decoded and/or decrypted before it is
presented to the user. The file itself is
unchanged on the disk. When the buffer is
subsequently saved to disk, a hook function
re-encodes the buffer before the actual disk write
takes place.

Eev.el is a simple Emacs Lisp library that lets
you treat portions of a text file as shell
commands, chunks of code for programming
languages or as hyperlinks; its intention is to
let people record into plain ASCII files their
interaction with the computer, and to let them
edit and play back any block of code in those
files easily. The hyperlinks can point to places
in manpages, Info pages and text or HTML files,
and they are seen as comments by all programming
languages; using them you can place pointers to
all relevant online sources of information inside
the code.

GNU TeXmacs is a free wysiwyw (what you see is what you want) editing platform with special features for scientists. The software aims to provide a unified and user friendly framework for editing structured documents with different types of content: text, mathematics, graphics, interactive content. TeXmacs can also be used as an interface to many external systems for computer algebra, numerical analysis, and statistics. New presentation styles can be written by the user and new features can be added to the editor using Scheme.

Gnutran is a simple, Emacs-based front-end to a number of machine translation engines available on the Web. It can send emacs buffers to a translation engine, request a translation (e.g. English to Portuguese) and display the result on a new window. GNUTRAN interoperates with emacs-based email agents such as VM-Mail and features a highly configurable interface, allowing easy set up of new translation pairs through Emacs' customization interface.

ics.el is a comint based Emacs major mode for
handling the text portion of communications with
internet chess servers such as FICS and ICC. It is
written in Emacs-Lisp and works best in
conjunction with a graphical interface such as
Xboard. It handles colour highlighting and
"buttonisation" (making certain portions of text
active so that, for example, you can challenge
opponents with a single mouse click) as well as
command recall and editing and automation of
commands based on regexps seen in the ICS output,
all highly customisable using Emacs lisp.

MIT/GNU Scheme is an implementation of the Scheme programming language, providing an interpreter, compiler, source-code debugger, integrated Emacs-like editor, and a large runtime library. MIT/GNU Scheme is best suited to programming large applications with a rapid development cycle. Recent versions of the system are supported on the following platforms: GNU/Linux, *BSD, OS/2, and Windows.

Proof General is a generic Emacs interface for proof assistants, suitable for use by pacifists and Emacs militants alike. It is supplied ready-customized for LEGO, Coq, and Isabelle. You can adapt Proof General to other proof assistants if you know a little bit of Emacs Lisp.